Assertion failed: (e > 0), function SslContext_t, file ssl.cpp, line 167.

I am trying to run my Rails app in SSL mode. I created a self-signed cert as follows:

openssl req -new -nodes -keyout server.key -out server.csr
openssl x509 -req -days 365 -in server.csr -signkey server.key -out server.crt

and I'm starting my app as such:

thin start --ssl --ssl-verify --ssl-key-file /Users/mark/certs/server.key --ssl-cert-file /Users/mark/certs/server.key -D -V

When I make a request, the server crashes with:

>> Using rack adapter
>> Thin web server (v1.3.1 codename Triple Espresso)
>> Debugging ON
>> Tracing ON
>> Maximum connections set to 1024
>> Listening on 0.0.0.0:3000, CTRL+C to stop
Assertion failed: (e > 0), function SslContext_t, file ssl.cpp, line 167.
Abort trap: 6

Am I doing something wrong?